One company's move to go virtual leads to I/O constraints

Computerworld - Austin Radiological Association is a quarter of the way toward virtualizing its server and desktop infrastructure, but the move has placed a strain on its networked storage and slowed application performance.

ARA, which provides diagnostic imaging services through 15 outpatient centers in central Texas, is trying out a new product from startup Zerto, which launched last year with an unusual approach to data protection. Instead of protecting data by replicating it offsite from storage arrays, it uses software to replicate the data within the virtual machines.

ARA's IT department has about 40 people managing almost 800TB of data. It has about 1,000 desktops for 800 employees along with 300 servers, about 25% of which are currently virtualized using VMware and Citrix XenServer.

ARA, which is part of a larger consortium of radiological imaging firms, had originally imagined itself moving to a private cloud, carving up its data center, selling services to its regional affiliates and becoming the "center of the universe." But that became complicated fast.

"We backed off that cloud marketing hype and decided to learn to crawl before we sprinted," said ARA CIO Todd Thomas. "We didn't see ourselves doing chargeback right away or auto provisioning of servers right away, because our processes weren't mature enough as an IT organization."

So ARA shifted its plan to virtualizing its data center, selecting Cisco's Unified Computing System (UCS) blade center as its server farm, and EMC and NetApp products for storage. But what Thomas didn't want to do is get locked into a particular vendor's data replication software.

"If I want to switch colocation providers, it's easier to migrate a virtual machine and not care about what the underlying storage platform is," Thomas said.

As with most companies, ARA's data replication scheme for business continuity and disaster recovery is based in its networked storage, which features both EMC Symmetrix DMX-4 950 and NetApp 3140 arrays. Replication in those arrays is performed at the block or file level, meaning data is either mirrored or copied to its offsite recovery facility 20 miles south of its primary data center in Austin. ARA uses both EMC's Symmetrix Remote Data Facility/Asynchronous (SRDF/A) and MirrorView software for data replication.

But when it began virtualizing its server and desktop environment, the strain of additional virtual machines overwhelmed its storage arrays' I/O bandwidth.

The ARA project started as a XenApp installation in which applications were going to be streamed down to Wyse Technology thin clients. "In that rollout, we ran into a number of hurdles that shifted our strategy to go more the VDI route than just the applications streaming route," Thomas said.

But an "unforeseen" explosion of virtual desktops created I/O performance problems. "We got about 70% of the way through the project and are now on hold," he said. Instead of 80% streaming applications and 20% VDI, ARA wound up implementing 80% virtual desktops and 20% streaming apps.

"The predominance of virtual desktops created a strain on our storage arrays we weren't anticipating," Thomas said. Not surprisingly, application performance began to suffer.